Space travel: Dual origins of light flashes seen in space

Light flashes are unusual visual phenomena that are observed in space and are caused by the interaction of energetic cosmic-ray particles with the human visual system. Using data gathered on board the Mir space station during the Sileye-2 experiment, we show here that there are two separate components of cosmic rays that cause these flashes: one due to heavy nuclei and one due to protons. This indicates that perception by an astronaut's visual apparatus could involve two complementary mechanisms.